Pop-on-cap assemblies having splay-resisting features and anti-splay features for spinal surgery with wide features allowing purposeful splay by trans-cap distal force

ABSTRACT

A spinal-surgery system having a receiver for receiving a rod and/or a receiver cap. The cap has a generally cylindrical body and a set of opposing splay-resisting flanges extending radially from the body. The receiver has arms each having an inner proximal protrusion at or adjacent the proximal end, and an inner sloped splaying surface distal of the proximal protrusion. Each cap flange has a proximal-facing cap splay-prevent surface, and a distal-facing cap pop-on surface. Each receiver proximal protrusion has a proximal-facing sloped receiver pop-on surface, and a distal-facing sloped receiver splay-prevent surface. The receiver pop-on surfaces are spaced so each cap pop-on surface contacts a respective receiver pop-on surface in operation. Each splaying revision surface extends distally and radially inward toward the longitudinal axis and into a cylindrical plane defined by an inner diameter of the cap. The cap inner diameter is greater than a rod width.

FIELD

The present disclosure relates to implants for use in spinal surgeriesgenerally and, more particularly to spinal systems including pop-on capimplants and the corresponding receivers, wherein the caps and receiversare configured such that (i) the caps can be popped on by intentionallysplaying receiver arms, (ii) the cap interfaces with the receiver afterbeing popped on to resist receiver-arm splay, and (iii) the caps canlater, for revision procedures, be removed readily from the receivers,by intentionally splaying receiver arms.

BACKGROUND

Spinal pathologies and disorders such as scoliosis, kyphosis, and othercurvature abnormalities, degenerative disc disease, disc herniation,osteoporosis, spondylolisthesis, stenosis, tumor and fracture may resultfrom factors including trauma, disease and degenerative conditionscaused by injury and aging. Spinal disorders typically result insymptoms including deformity, pain, nerve damage, and partial orcomplete loss of mobility.

Non-surgical treatments, such as medication, rehabilitation and exercisecan be effective, however, may fail to relieve the symptoms associatedwith these disorders.

Surgical treatment of these spinal disorders includes correction,fusion, fixation, discectomy, laminectomy and implantable prosthetics.

Surgical rods are used commonly in correcting spinal abnormalities.Pedicle-screw assemblies are often used to facilitate securement of oneor more spinal rods relative to the spine. Pedicle-screw assembliesinclude a bonescrew attached to a rod-receiving receiver. The bonescrewsare attached to patient vertebrae, and the receivers receive portions ofthe spinal rod.

Receivers typically have opposing arms extending proximally from adistal base, forming a rod-receiving cavity between them. The arms oftenundesirably splay away from each other during locking of the receiver tothe rod. Various prior methods have been used to prevent or limit thissplay.

Another need relates to the occasional need to revise a previouslyimplanted construct. Removing set-screws, to release or adjust the rodfor these procedures, can be difficult.

SUMMARY

Systems and processes of the present disclosure relate generally toimplants for use in spinal surgeries and, more particularly, to systemshaving cap implants configured to (i) pop by fully distal motion ontocorresponding rod receivers, (ii) prevent splay of receiver arms wheninstalled, and (ii) be removed readily from the receivers in potentialrevision surgeries.

In one aspect, the present disclosure provides a system for use inspinal surgery. The system including a cap having a generallycylindrical body and a set of opposing splay-resisting flanges extendingradially from the body. The system also includes a receiver havingopposing arms spaced equally from a longitudinal axis of the receiver,each arm extending to a respective proximal end from a common distalbase, each arm having an inner proximal protrusion at or adjacent theproximal end, and each arm having an inner sloped splaying surfacedistal of the proximal protrusion. Each cap flange has a proximal-facingcap splay-prevent surface, sloped proximally and radially outward, and adistal-facing cap pop-on surface. Each receiver proximal protrusion has(i) a proximal-facing sloped receiver pop-on surface extending distallyand radially inward toward the longitudinal axis, and (ii) adistal-facing sloped receiver splay-prevent surface extending distallyand radially inward toward the longitudinal axis. The receiver pop-onsurfaces are spaced from each other such that each cap pop-on surfacecontacts a respective one of the receiver pop-on surfaces when the capis centered on the longitudinal axis and moved distally to contact thereceiver. Each splaying revision surface extends distally and radiallyinward toward the longitudinal axis and into a cylindrical plane definedby an inner diameter of the cap. The inner diameter of the cap isgreater than a width of a spinal-correction rod that the receiver isconfigured to hold in use of the system.

The inner diameter of the cap is between about 0.5 mm and about 2.0 mmlarger than an outer diameter of the spinal-correction rod, in variousembodiments.

In some cases, each splaying surface extends radially inward into thecylindrical plane by a radial distance of between about 0.5 mm and about2.0 mm short of an outer diameter of the spinal-correction rod.

Each sloped splaying surface can extend at an angle with respect to ahorizontal reference frame of between about 35 degrees and about 55degree.

In various embodiments, each cap splay-prevent surface extends at a capsplay-prevent angle with respect to a horizontal reference frame ofbetween about 5 degrees and about 75 degrees. And each receiversplay-prevent surface extends at a receiver splay-prevent angle withrespect to the horizontal reference frame of between about 5 degrees andabout 75 degrees. Each cap splay-prevent angle can be between about 10degrees and about 45 degrees, and each receiver splay-prevent angle isbetween about 10 degrees and about 45 degrees.

In some cases, each receiver pop-on surface extends at a receiver pop-onangle with respect to a horizontal reference frame of between about 50degrees and about 80 degrees. The opposing flanges extend radially fromthe body along a first radial line of the body. The cap has a set ofopposing wings extending radially from the body along a second radialline of the body orthogonal to the first radial line. And the receiverpop-on surfaces are spaced from each other such that each cap pop-onsurface contacts a respective one of the receiver pop-on surfaces whenthe cap is centered on the longitudinal axis, with the cap wings alignedbetween the receiver arms, and moved distally to contact the receiver.In various embodiments, each receiver arm extends between opposinglateral edges, and lateral edges of each arm, of the set of arms, arespaced by an inter-arm distance from an adjacent lateral edge of theother arm, of the set of arms. And each cap wing has a width that isgenerally equal to, but slightly smaller than, the inter-arm distance,to allow the cap wing to be slid distally between the receiver arms andcontact both adjacent lateral arm edges when the wings are positionedbetween the arms and torque is applied to the cap.

Each receiver arm in some cases has an inner surface extending from adistal portion to a proximal portion adjacent said proximal end of thearm. The proximal portion of each inner surface defines a protrusioncavity receiving the cap flange when the cap is popped onto thereceiver.

The cap further includes opposing anti-rotation wings extending frombody generally orthogonally to a line along which the flanges extendfrom the body, in various embodiments.

In another aspect, the present disclosure provides a system for spinalsurgery including a cap for being popped onto a rod receiver, the caphaving a generally cylindrical body, and a set of opposing flangesextending radially from the body. The receiver has opposing arms spacedequally from a longitudinal axis of the receiver, each arm extending toa respective proximal end from a common distal base, each arm having aninner proximal protrusion at or adjacent the proximal end, each armhaving an inner sloped splaying surface distal of the proximalprotrusion, each receiver proximal protrusion having (i) aproximal-facing sloped receiver pop-on surface extending distally andradially inward toward the longitudinal axis, and (ii) a distal-facingsloped receiver splay-prevent surface extending distally and radiallyinward toward the longitudinal axis, the receiver pop-on surfaces beingspaced from each other such that each cap pop-on surface contacts arespective one of the receiver pop-on surfaces when the cap is centeredon the longitudinal axis and moved distally to contact the receiver, andeach splaying revision surface extending distally and radially inwardtoward the longitudinal axis and into a cylindrical plane defined by aninner diameter of the cap. Each cap flange has a proximal-facing capsplay-prevent surface, sloped proximally and radially outward, and adistal-facing cap pop-on surface.

The system of this aspect can have any of the features described abovein connection with the first embodiment.

In yet another aspect, the present disclosure provides a system for usein spinal surgery, including a receiver for receiving a pop-on cap, thereceiver having opposing arms spaced equally from a longitudinal axis ofthe receiver, each arm extending to a respective proximal end from acommon distal base, each arm having an inner proximal protrusion at oradjacent the proximal end, and each arm having an inner sloped splayingsurface distal of the proximal protrusion. The cap has a generallycylindrical body, and a set of opposing flanges extending radially fromthe body, each cap flange having a proximal-facing cap splay-preventsurface, sloped proximally and radially outward, and a distal-facing cappop-on surface. Each receiver proximal protrusion has (i) aproximal-facing sloped receiver pop-on surface extending distally andradially inward toward the longitudinal axis, and (ii) a distal-facingsloped receiver splay-prevent surface extending distally and radiallyinward toward the longitudinal axis. The receiver pop-on surfaces arespaced from each other such that each cap pop-on surface contacts arespective one of the receiver pop-on surfaces when the cap is centeredon the longitudinal axis and moved distally to contact the receiver. Andeach splaying revision surface extends distally and radially inwardtoward the longitudinal axis and into a cylindrical plane defined by aninner diameter of the cap.

The system of this aspect can have any of the features described abovein connection with the first embodiment.

Details of various aspects of the disclosure are set forth in theaccompanying drawings and description below. Other features, objects,and advantages of the technology will be apparent from the description,drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a cap and receiver system, according toa first embodiment of the present technology;

FIG. 2 is a side cross section of the system taken along line 2-2 ofFIG. 1, showing the cap being lowered onto the receiver;

FIG. 3 is a is a perspective view of the maneuver of FIG. 2;

FIG. 4 is a perspective view showing the cap contacting the receiver,prior to being popped on;

FIG. 5 is a side cross section taken along line 5-5 of FIG. 4;

FIG. 6 is a side cross section showing the cap being popped on, the capforcing receiver arms to splay slightly to allow the cap to movedistally to a locking position in the receiver;

FIG. 7 is a side cross section taken along line 7-7 of FIG. 8, showingthe cap popped onto the receiver;

FIG. 8 is a side view of the state shown in FIG. 7;

FIG. 9 is a top, plan, view of the state of the same;

FIG. 10 is a side cross section of a cap and receiver according to asecond embodiment of the present technology;

FIG. 11 is a perspective view of a cap and receiver according to a thirdembodiment of the present technology;

FIG. 12 is a side cross section of the system of the third embodiment,taken along line 12 of FIG. 11, having a setscrew threaded into the cap;

FIG. 13 is a top view of the arrangement of FIG. 12;

FIG. 14 is a perspective view of the arrangement of FIGS. 12 and 13;

FIG. 15 is a perspective view of a cap and receiver, prior to poppingthe cap onto the receiver, according to a fourth embodiment of thepresent technology;

FIG. 16 is a side cross section of the system of the fourth embodiment,taken alone line 16-16 of FIG. 15, with the cap having been popped ontothe receiver; and

FIG. 17 is a perspective view of the embodiment and state of FIG. 16.

DETAILED DESCRIPTION

The present description presents three primary embodiments, each havingrelated features and including various sub-embodiments. Each of theembodiments relate to systems including surgical caps configured to (i)pop onto a rod receiver, (ii) lock into the receiver to resist receiverarm splay, and (ii) be removed selectively from the receiver, by userapplication of a relatively low torque or force, and to thecorresponding receiver configured to facilitate the same. Embodimentsalso describe instruments used to effect these maneuvers.

Turning now to the drawings, and more particularly to the first figure,FIG. 1 shows a perspective view of a first embodiment of a cap andreceiver system, indicated generally by reference numeral 100.

The system 100 includes a receiver implant 110 and a corresponding capimplant 150. The receiver 110 can be referred to by various terms, suchas tulip or screw head. The receiver 110 and cap 150 have correspondinggeometries, for mating together by popping the cap 150 onto the receiver110. The cap is popped onto the receiver 110 by fully-distally-directedmotion of the cap 150, along a longitudinal (proximal-to-distal) axis 30of the receiver, down onto the receiver 110.

The receiver 110 has opposing arms 130 extending proximally from adistal base 120. The base 120 is configured for receiving or beingconnected to a bone screw (not shown) for anchoring the system 100 to apatient vertebra. The opposing receiver arms 130 define a rod-receivingcavity between them. A rod 10 is shown positioned in the cavity. The rod10 can be considered a part of the system 100, or used with it.

FIG. 2 is a side cross section of the system 100 taken along line 2-2 ofFIG. 1, showing the cap 150 being lowered onto the receiver 110.

The cap 150 has an internal thread 152 for receiving a setscrew inoperation of the system 100. The setscrew can be loaded before or afterthe cap 150 is popped into the receiver 110. An example setscrew 20 isshown in FIGS. 12-14, illustrating a related but distinct embodiment ofthe present technology. In each embodiment, as with the rod 10, thesetscrew 20, can be part of the system 100, or simply used with it. Anyof the components described—cap, receiver, rod, setscrew, bonescrew (notshown), cap-removing tool or instrument (not shown), etc.—can be made,sold, distributed, stored, or otherwise provided together, such as in asurgical kit or set.

In various embodiments, each receiver arm 130 has a proximal flange orprotrusion 132 and a distal protrusion or shelf 133 extending radiallyinward from a primary wall 131. The protrusions 132, 133 define acap-receiving compartment or cavity 136 between them.

The proximal protrusion 132 has opposing sloped receiver pop-on surfaces134. In various embodiments, each receiver pop-on surface 134 is aproximal surface of the protrusion 132 extending radially inward anddistally. Each receiver pop-on surface 134 may in any portion of it berounded, curved, beveled, or otherwise not perfectly straight, includingat one or both of a distal edge and a proximal edge of the surface 134and intermediate the edges.

The cap 150 has opposing cap pop-on/splay-resisting wings or flanges160. The flanges 160 each extend along a common radial line of the cap150 from a primary wall 161 of the cap 150. Each flange 160 is invarious embodiments positioned at a distal end of the cap 150.

Each flange 160 has a pop-on surface 162, which in various embodimentsis at a radially extreme and distally extreme portion of the flange 160.

With further reference to FIG. 2, each cap pop-on surface 162 is angledor sloped in various embodiments. The cap pop-on surfaces 162 may berounded, curved, beveled, or otherwise not perfectly straight, at anypoint, including at one or both edges (distal and proximal edges) andintermediate the edges.

The cap 150 and receiver 110 are sized and shaped such that when the cap150 is axially 30 centered over, and moved distally into contact with,the receiver 110, with cap anti-rotation flanges or wings 170 alignedover inter-arm gaps, the cap pop-on surfaces 162 contact thecorresponding receiver pop-on surfaces 134.

The flanges 160 and wings 170 are in various embodiments generallyco-planer. Benefits of having them on the same plane, or close to eachother planarly, include the ability to keep the height down. A smallerprofile cap requires less material, is lighter, and can have thesequalities without compromising strength for the describedfunctionalities.

The receiver and cap pop-on surfaces 134, 162 are angled or sloped suchthat after the cap 150 contacts the receiver 110 at the surfaces 134,162, and the cap is forced further distally, each cap pop-on surface 162slides distally along the corresponding receiver pop-on surface 134. Theradially outward-facing cap pop-on surfaces 162 pushing on theinward-facing receiver pop-on surfaces 134 forces the arms 130 to moveslightly away from each other, or splay. This allows the cap flanges 160to clear proximal receiver protrusions 132, to lock into the receiver110, as the cap is moved further distally.

As indicted in FIG. 2, each receiver pop-on surface 134 extends at anangle 115, and each corresponding cap pop-on surface 162 extends at anangle 163, with respect to a horizontal reference frame.

Each cap pop-on surface 162 extends in various embodiments at the angle163 being between about 45 degrees and about 85 degrees. In some cases,the range is smaller, such as between about 50 degrees and about 80degrees. These are only examples, and the cap 150 can be designed sothat the angle 163 has any value or range within these ranges, or beyondthese ranges. The angle 163 is in various embodiments at least between 0degrees and 90 degrees.

In a contemplated embodiment, the cap pop-on surface 162 is a distal,proximally extreme corner of the cap.

For embodiments in which the cap 150 has an angled, sloped, rounded, orbeveled, pop-on surface 162, benefits of the cap pop-on surface 162having these angles, or related rounding or beveling, with sufficientlycorresponding angulation of the receiver pop-on surface 134, include thesurface 162 being able to cause the receiver arms 130 to splay when thesurface 162 is pushed distally against the receiver pop-on surface 134with sufficient force, to push the receiver pop-on surface 134, and sothe receiver arms 130 by an amount sufficient to allow the cap flange160 to pass distally beyond the receiver proximal protrusion 132.

Each receiver pop-on surface 134 extends in various embodiments at theangle 115 being between about 45 degrees and about 85 degrees. In somecases, the range is smaller, such as between about 50 degrees and about80 degrees. These are only examples, and the receiver 110 can bedesigned so that the angle 115 has any value or range within theseranges, or beyond these ranges. The angle 115 is between 0 degrees and90 degrees.

Benefits of the receiver pop-on surface 134 having such angle 115include the surface 134 being configured to cause the receiver arms 130to splay, when the cap pop-on surface 162 is pushed distally against thereceiver pop-on surface 134, by an amount sufficient to allow the capflange 160 to pass distally beyond the receiver proximal protrusion 132.The angle 115 is selected to facilitate the maneuver in response to apre-determined distal force on the cap 150 below an undesirable force.The system 100 is designed so that it is not too difficult for a user topop the cap 150 into the receiver 110.

System characteristics facilitating the pop-on maneuver can also includethickness and material of portions or all of the receiver arms 130, andin some cases size, shape, and material of the receiver base 120, suchas proximal portions of the base 120. The receiver 110 can also besized, shaped, and have material allowing the arms to spring back,toward their original position, after the cap flanges 160 have passeddistally beyond the proximal receiver protrusion 132.

In various embodiments the cap 150 and receiver 110 are configured suchthat angles 165, 115 of the respective pop-on surfaces 162, 134 aregenerally the same, or within a predetermined angle, or percentage ofangulation, from each other. The surfaces can be configured such thatthe correspondence provides robust, or maximizes, surface-to-surfacecontact, so that force applied to the receiver pop-on surface 132 by thecap pop-on surface 162 is distributed, as opposed to being more of apoint force.

FIG. 2 also shows that each flange 160 also has a proximally facing caplock, or splay-resisting, surface 164. The receiver 110 has acorresponding, distally facing, receiver lock, or splay-resisting,surface 138. Function of these surfaces is described further below,including in connection with FIG. 7.

FIG. 3 is a is a perspective view of the maneuver of FIG. 2, showing thecap 150 being lowered onto the receiver 110 along the receiverlongitudinal axis 30. This view shows the cap anti-rotation flanges orwings 170 extending radially outward generally perpendicular to adirection that the cap pop-on flanges 160 extend radially outward. Thecap wings 170 are as mentioned aligned over inter-arm 130 gaps for thepop-on maneuver.

FIG. 4 is a perspective view showing the pop-on cap 150 moved furtherdistally to contact the receiver 110. As shown, as the cap 150 is movedinto contact with the receiver 110, the opposing anti-rotation wings 170of the pop-on cap 150 become disposed between adjacent arms 130 of thereceiver 110.

As the cap 150 is pushed further distally with respect to the receiver110, forces from the cap pop-on surfaces 162 of cap flanges 160 againstthe receiver pop-on surfaces 134, push the receiver pop-on surfaces 134,and so the receiver arms 130, splay, moved radially away from eachother, or laterally away from the longitudinal axis 30.

FIG. 5 is a side cross section taken along line 5-5 of FIG. 4. Startingof the forced arm 130 splaying, as the cap pop-on surfaces 162 arepushed against the receiver pop-on surfaces 134, is indicatedschematically in FIGS. 4 and 5 by opposing radial arrows.

FIG. 6 is a side cross section showing the pop-on cap 150 having beenpushed further distally with respect to the receiver 110. The opposingreceiver arms 130 are shown slightly splayed, having been pushed apartby the radially outward forces effected at the receiver pop-on surfaces134 by the distal pushing from the cap pop-on surfaces 164.

FIG. 7 is a side cross section, taken along line 7-7 of FIG. 8, showingthe pop-on cap 150 after it has been forced further distally withrespect to the receiver 110, from the state of FIG. 6. After the pop-oncap flange 160 moves distally past the proximal receiver protrusion 132,the mentioned cap-to-receiver pop-on force ceases, and so the receiverarms 130 spring back toward their original position. That is, the forcedsplay is relieved. The receiver arms 130 moving back, radially inward,is indicated by opposing arrowed lines in FIG. 7.

After the pop-on cap flange 160 clears the proximal receiver protrusion132, and the receiver arms 130 are thereby allowed to move back in, nolonger being held apart by the cap flanges 160, the cap flanges 160become disposed within the cap-receiving cavity 136 of the receiver 110.

The maneuver also positions each of the opposing proximally facing capsplay-resisting surfaces 164 adjacent and facing a correspondingreceiver splay-resisting surface 138. The two surfaces are configured(sized, shaped, positioned, oriented, etc.) to engage, or interlock. Theinterlock prevents the receiver arms 117 from moving away from eachother, or splaying, undesirably after the engagement. In someembodiments, the cap 150 and receiver 110 are configured such that thesurfaces 164, 138 end up generally flush against each other, or at leastflush along one or more portions of the surfaces 164, 138.

Each receiver splay-resisting surface 138 extends in various embodimentsat an angle 117 with respect to the horizontal reference frame ofbetween about 5 degrees and about 75 degrees. In some cases, the rangeis smaller, such as between about 10 degrees and about 45 degrees. Theseare only examples, and the receiver 110 can be designed so that theangle 117 has any value or range within these ranges, or beyond theseranges. The angle 117 is at least between 0 degrees and 90 degrees.

Benefits of the receiver splay-resisting surface 138 having theseangles, with sufficiently corresponding angulation of the capsplay-resisting surface 164, include the surface 138 being angledaggressively enough to create a robust connection with thesplay-resisting surface 164 of the cap 150 for resisting receiver armsplay, or, partially locking the arms 130 against unwanted arm splay,such as in tightening of the set screw in the receiver 110 and onto therod 10, but slight enough such that removal of the cap 150 by splayingthe receiver arms 130 intentionally, in a potential revision procedure,after the initial surgery implanting the system 100 (e.g., years later),is relatively easy with sufficient force separating the arms 130.

Variables for facilitating the robust connection and/or the relativelyeasy release can also include length and width of the surfaces 164, 138,and material of the surfaces 164, 138, of the cap flange 160 andreceiver protrusion 132.

Each cap splay-resisting surface 164 extends in various embodiments atan angle 165 with respect to the horizontal reference frame of betweenabout 5 degrees and about 75 degrees. In some cases, the range issmaller, such as between about 10 degrees and about 45 degrees. Theseare only examples, and the cap 150 can be designed so that the angle 165has any value or range within these ranges, or beyond these ranges. Theangle 165 is at least between 0 degrees and 90 degree.

Benefits of the cap splay-resisting surface 164 having these angles,with sufficiently corresponding angulation of the receiversplay-resisting surface 138, include, again, the surface 164 beingangled aggressively enough to create a robust connection with thesplay-resisting surface 138 of the receiver 110, to lock the receiverarms 130 against unwanted splay, such as in tightening of the set screwin the receiver 110 and onto the rod 10, but slight enough for removalof the cap 150 by intentional splaying of the receiver arms 130 to berelatively easy with sufficient force separating the arms 130.

In various embodiments, the cap 150 and receiver 110 are configured suchthat angles 165, 117 of the respective splay-resisting surfaces 164, 138are generally the same, or within a predetermined angle or percentage ofangulation from each other. An entirety, or portions of the surfaces insome embodiments end up flush against each other when the system 100 isin the locked position shown in FIGS. 7-9.

While the splay-resisting surfaces 138, 164 are shown contacting in FIG.7, in various embodiment, this contact is not automatically fosteredsimply by the cap flange 160 clearing the proximal receiver protrusion132 and entering the cap-receiving cavity 136. The receiver arms 130,including the cap-receiving cavities 136 defined partially thereby, areas mentioned sized and shaped to allow the cap flanges 160 to, uponclearing the proximal receiver protrusions 132, become disposed in thecavities 136. For embodiments in which the receiver 110 includes thedistal protrusion 133, the distal protrusions 133 of the receiver 110must be sufficiently spaced from the proximal protrusion 132 to allowclearance for the disposals. In a contemplated embodiment, the receiver110 does not include the distal protrusion or shelf 133, or it is lesspronounced.

In assembling of the system 100, after the cap flanges 160 of the cap130 clear the proximal receiver protrusion 132, the cap can be movedproximally by threading the setscrew within the cap 150. This is doneusing a setscrew driver (not shown). An example setscrew 20 is shown inFIG. 12, in connection with another embodiment of the presenttechnology. The setscrew is threaded distally through the pop-on cap 150threadform 152 until a distal tip of the setscrew contacts the rod 10positioned between the arms 130 of the receiver 110. At this point,relative position between the setscrew and the rod is generally fixed.As the setscrew is threaded further through the cap 150, the cap ismoved proximally by the continued threading action, as the setscrewgenerally does not move any further distally with respect to the rod 10.

The pop-on cap 150 is moved proximally in this way until the cap flanges160 contact the proximal receiver protrusion 132 robustly. Therespective splay-resisting surfaces 138, 164 thereby engage and are keptin contact. A component of forces that the proximally facingsplay-resisting surface 164 of the cap 150 exerts on the distally facingsplay-resisting surface 138 of the receiver 110 is radially inward,preventing the receiver lock surfaces 138 from moving away from eachother, and thereby preventing splay of the arms 130.

FIG. 8 is a side view of the system state shown in the cross sectionFIG. 7. The view shows the anti-rotation wings 170 of the pop-on cap 150disposed between respective arms 130 of the receiver 110. The wings 170keep the pop-on cap 150 from rotating in either direction, such as whena user is tightening/loosening a setscrew into/out of the cap 150.

More particularly, with reference to plan view of FIG. 9, when thesetscrew is turned in the installed cap 150, the cap 150 is kept fromrotating by edges 900 (four of them, e.g.) of the two anti-rotationwings 170 contacting adjacent edges 910 (four of them, e.g.) of thereceiver arms 130.

A user may need to remove the pop-on cap 150, after the initial surgeryimplanting the system 100 (e.g., years later), in a revision procedure,in which the rod 10 needs to be removed or adjusted. A cap-removinginstrument or tool (not shown) can be used. In various embodiment, theinstrument has a distal end or ends sized and shaped to fit within a gap135, defined between the proximal end of the receiver 110 and theproximal end of the cap 150, and effect intentional receiver splay byforcing the arms 130 laterally outward while positioned in the gap 135.The gap 135 is called out in FIGS. 7-9. Alternately, an instrument canapply lateral forces by applying a force to the interior walls of thereceiver arms 130.

The proximal end of the receiver 110 include a proximal inner surface,adjacent and in some cases defining the gap 135. The surface facilitatesthe revision splaying. The proximal inner surface can be slanted, forinstance, so that the splaying instrument when pushed distally againstthe surface slides along the proximal inner surface thereby forcing theproximal inner surfaces, and so the arms 130, radially outward. In acontemplated embodiment, the proximal inner surface of the receiver arms130 has a notch, slot, or other element that the instrument can secureor connect to in order to facilitate robust contact between theinstrument and surface, and forcing of the proximal inner receiversurface radially outward. In another contemplated embodiment, the innersurface is not slanted, or only slanted only slightly, and theinstrument upon being placed in the gap 135 forces the arms 130 apart byapplying force radially outward on the walls, without any, or withoutmuch, relative siding between the instrument and the proximal innerreceiver surface.

As the arms 130 splay, the splay-resisting interfaces 136, 164 arepushed apart, namely the receiver splay-resisting surfaces 136 areforced to move radially outward, along and then off of the capsplay-resisting surfaces 164. The cap 150 is then free from the receiver110, and can be removed in the proximal direction from the receiver 110.In various embodiments, the instrument has a capture design forgrasping, engaging, or otherwise persuading the cap 150 to moveproximally, out of the receiver 110, while the arms 130 are splayed bythe instrument. Or a separate cap removing instrument, such as one thatcan fit within, around, or aside of the splaying instrument, canpersuade the cap 150 proximally out of the receiver 110. Such removingfeature or instrument can have an external thread, for instance, forengaging with the internal thread of the cap 150.

With continued reference to the three main embodiments of the presentdisclosure, FIG. 10 shows a system 1000 according to the second mainembodiment. FIG. 10 shows a side cross section of an alternative pop-oncap 1050 and receiver 1010, according to this embodiment.

The pop-on cap 1050 and receiver 1010 of this embodiment is in many wayslike the cap and receiver 150, 110 of the first main embodiment, ofFIGS. 1-9. One primary distinction is that the pop-on cap 1050 of thisembodiment is designed to have a larger inner diameter (ID) 1052 (and inmost cases also, then, a larger outer diameter (OD)) than that of thecap 150 of the first embodiment. The cap 150 of the first embodiment isin some cases sized to receive a standard setscrew. The cap 1050 of FIG.10 is in various embodiments sized to receive a unique setscrew, havinga larger-than-standard outer diameter, or thread diameter.

As another important distinction, due to the larger cap 1050 in thisembodiment, the receiver 1010 is also larger to accommodate the cap1050. For example, the arms 1030 are spaced apart farther from eachother for the system 1000 of this embodiment as compared to separationbetween the arms 130 of the receiver 110 of the system 100 of the firstembodiment.

Another primary distinction between the system 1000 of FIG. 10 and thesystem 100 of FIGS. 1-9 is that the receiver 1010 of this embodiment hasa pronounced inward-and-downward-slanting or -sloped wall 1040. The wall1040 extends radially inward farther than the ID 152 of the pop-on cap1050, as shown in FIG. 10. That is, each of the walls 1040 extenddistally and radially into a cylindrical plane defined by the ID of thecap 1050.

In various embodiments, the cap ID 1052 is between about 7.0 mm andabout 8.0 mm. In various embodiments, each slanted wall 1040 extendsradially inward to within the cylindrical plane of the cap OD 1052 by aprotruding distance 1042 of between about 5.0 and about 6.0 mm.

The slanted wall 1040 extends at an angle 1044 with respect to ahorizontal reference frame. In various embodiments, the wall 1040 isoriented at an angle 1044 of between about 30 degrees and about 60degrees. In some cases, the range is smaller, such as between about 35degrees and about 55 degree, or between 40 and 50 degrees. These areonly examples, and the cap 150 can be designed so that the angle 163 hasany value, such as about 45 degrees, or range within said ranges, orbeyond these ranges. The angle 1044 is between 0 degrees and 90 degrees.

For removing the cap 1050 of this embodiment, such as in a revisionprocedure, the cap ID 1052 is sized, and the slanted wall 1040 sized,oriented, and positioned, to permit a splaying instrument or tool (notshown) to extend distally through the central cavity of the cap 1050 andinto contact with the slanted wall 1040.

For revision procedures, a surgeon can remove the internal setscrew 20and then load the splaying instrument through the cap to contact theinternal tapered portion 1040 such as to splay the walls open forremoval of cap 1050.

For cases in which the instrument is used while the rod 10 is stillpositioned in the receiver 110, the instrument may have a hollow sizedto receive the rod 10. In this way, the rod 10 does not interfere withthe function of contacting and pressing sufficiently against the slantedsurface 1040 by the splaying instrument. Or the splaying instrument mayhave two or more arms or prongs extending distally from a body of thetool such that the rod 10 does not interfere with the instrumentcontacting and pushing against the receiver splay surfaces 1040.

After the distal tips of the splaying instrument contact the receiversplay surfaces 1040, the instrument is pushed further distally, applyingmore force to the surfaces 1040. The tips in this slide along thesurfaces 1040 as radially outward components of the force applied by thetips onto the surfaces 1040 cause the surfaces 1040, and so the receiverarms 1030 to move away from each other, or splay.

As the arms 1030 splay, the splay-resisting interfaces 1036, 1064 arepushed apart, the cap locking surfaces 1064, and so the cap flanges onwhich the locking surfaces are on, become free from the receiver armlocking surfaces 1038, and so free of the receiver proximal protrusionson which the arm locking surfaces are on. The freedom allows the cap1050 to be removed in the proximal direction from the receiver 1050. Invarious embodiments, the instrument has a capture design for grasping,engaging, or otherwise persuading the cap 1050 to move proximally, outof the receiver 1010, while the arms 1030 are being splayed by theinstrument. Or a separate cap removing instrument or tool, such as onethat can fit within, around, or aside of the splaying instrument, can beused.

Any other features of the system 1010 of this embodiment can be similaror identical to corresponding features of the system 100 described inconnection with FIGS. 1-9.

Turning to the third main related embodiment, FIGS. 11-14 show a system1100 again having a pop-on cap 1150 and receiver 1110. FIG. 11 isperspective view showing the system 1100 after the cap 1150 has beenpopped onto the receiver 1110.

For initially securing the cap 1150 to the receiver 1110, the cap 1150is lowered toward the receiver 1110 along a system axis 40. The cap 1150is orientated for the maneuver with opposingrotation-preventing/rotation-resisting wings 1152 aligned, orpositioned, over wing-receiving cavities 1134 of the receiver 1110. Thecap 1150 is popped onto the receiver 1110 in a manner similar to thepop-on maneuver described above in connection with the embodiments ofFIGS. 2-7. The cap 1150 and receiver 1110 are further configured (e.g.,sized and shaped) such that splaying of the receiver arms 1130 isresisted, in a manner similar to how splaying of the receiver 110 isresisted after cap 150 installation was described in connection with theembodiments of FIGS. 1-9 and 10.

FIG. 12 shows receiver and cap splay-resisting-resisting, or locking,surfaces 1138, 1164, like those of the embodiments of FIGS. 1-9 and 10.These engage upon popping on the cap 1150, and in some cases only afteralso threading the setscrew sufficiently into the cap 1150, as describedabove regarding other embodiments.

The cap rotation-resisting/splay-promoting wings or protrusions 1152 areconfigured to prevent the cap 1050 from rotation in one direction, andto resist the cap from rotating in another direction, after the cap 1150has been popped onto the receiver 1110 and when torque is applied to thecap 1050. Namely, for instance, the wings 1152 are configured (e.g.,sized and shaped) to prevent the cap 1150 from rotating in a firstdirection with respect to the receiver 1110—clockwise in the example ofFIG. 11. And the wings 1152 are configured in various embodiments toresist rotating of the cap 1150 in the oppositedirection—counterclockwise in the example of FIG. 12).

Proximal ends of receiver arms 1130 have shapes corresponding to shapingof the wings 1152 to effect the prevention and resistance functions. Theproximal end of each arm 1130 includes the wing-receiving cavity 1134sized and shaped to receive the cap wing 1152.

For the rotation-preventing function, rotation of the cap 1150 withrespect to the receiver 1110 is prevented by a cap rotation-preventingsurface 1155 of the wing 1152 contacting a corresponding receiverrotation-preventing surface 1132 of the proximal end of the receiver1110. In various embodiments, the cap rotation-preventing surface 1155extends radially from a cylindrical body 1157 of the cap 1150. Theprevention is promoted further by splay-resisting functionality, likethat of the first wo main embodiments, keeping the arms 1130 fromsplaying.

Each of the receiver and cap anti-rotation surfaces 1132, 1155 mayextend generally orthogonal to a tangent 1159 of the cylindrical body1157. In other embodiments, either or both are angled by more or lessthan 90 degrees with respect to the tangent, such as within a range ofabout 75 degrees to about 90 degrees.

Further regarding the resisting functionality, while the cap wings 1152and cavity 1134 are configured such that rotation in the first direction(e.g., clockwise) is prevented altogether, rotation in the seconddirection (counterclockwise) is only resisted. That is, rotation of thecap in the receiver is hindered, but possible in response to sufficienttorque placed on the cap in the second direction.

The receiver rotation-preventing surface 1132 can extend at generallythe same or similar angle as the cap rotation-preventing surface 1155.The surfaces 1155, 1132 can be generally, or close to, flush with eachother, for instance, when the cap 1150 is popped onto the receiver 1110.

The opposing rotation-preventing/rotation-resisting wings 1152 invarious embodiments have shape that may be referred to as a teardrop, asshown in FIG. 11, or similar descriptive terms, as the wing profile canbe generally demi- or half-teardrop shaped, such as shown in thefigures. The shape in various embodiments includes a first, caprotation-resisting, surface 1156 extending at a slighter angle 1158 fromthe body 1157 of the cap 1150, as compared to an angle (e.g., 90degrees) at which a second, cap rotation-preventing, surface 1155extends from the cap body 1157. A receiver rotation-resisting surface1136 may be angled to the same or similar corresponding disposition,promoting robust contact between the surfaces 1156, 1136, at least whentorque in the second direction (e.g., counterclockwise) is applied tothe installed cap 1150.

The cap rotation-resisting surface 1156 may extend, for instance, at anangle 1158 of between about 10 degrees and about 45 degrees, withrespect to the cap body tangent 1159. The angle 1158, which may begreater or smaller than this range, is configured (e.g., sized, shaped,and oriented) such that the receiver rotation-resisting surface 1156interfaces with a corresponding wall 1136 of the receiver gap 1134 whentorque is applied in the second direction (e.g., counterclockwiselocking down, distally, in FIG. 12) to the cap 1150. As the torque isapplied, the surface-to-surface 1156, 1136 interfacing resists rotatingof the cap 1150 in the second direction with respect to the receiver1110, but does not resist rotation of the cap 1150 in the seconddirection with respect to the receiver 1110 completely.

Torque can be applied to the cap 1150 in any of a variety of ways toforce intentional splay of the arms 1130. The system 1100 can include orbe used with an instrument or tool (not shown) configured at its distalend to engage a proximal portion of the wings 1152, for instance, andapply at least said pre-determined amount of torque to the cap 1150 inthe second direction (e.g., counterclockwise), the force beingsufficient to overcome friction between the rotation-resisting surfaces1156, 1136. The cap surface 1156 can thereby slide with respect to thereceiver surface 1136, as described, enabling the cap 1150 to rotatewith respect to receiver 1110, thereby splaying the arms 1130 for capremoval. As can be seen in FIGS. 11 and 14, the proximal surface of thewings 1152 can extend higher (farther proximally) than an adjacentproximal surface of the receiver arms 1130. The exposed proximal portionof the cap wings 1152 provides real estate that the instrument caninterface with to apply torque to the cap 1150 in the second direction.The instrument can apply torque against the portion of the anti-rotationsurfaces 1155 of the wings 1152 extending above the arms 1130, forinstance.

The surfaces 1156, 1136 are configured such that, upon application of atleast a predetermined amount of torque to the cap 1150 in the seconddirection, the cap 1150 rotates in the second direction with respect tothe receiver 1110, with the rotation-resisting surface 1156 of the cap1150 sliding along the rotation-resisting surface 1136 of the receiver1110.

A component of forces that the cap rotation-resisting surfaces 1156apply to the receiver rotation-resisting surfaces 1136, sliding in thesecond direction (e.g., counterclockwise) along the receiverrotation-resisting surfaces 1136, is a radial force. As the radial forceis applied to the receiver rotation-resisting surfaces 1136, and therebyto the receiver arms 1130, the arms 1130 are intentionally splayed.

As the receiver arms 1130 of this embodiment are splayed intentionally,the splay-resisting interfaces 1138, 1164 are pushed apart, namely thereceiver splay-resisting surfaces 1138 are forced to move radiallyoutward, along and then off of the cap splay-resisting surface 1164. Thecap 1150 is then free from the receiver 1110, and can be removed in theproximal direction from the receiver 1110. In various embodiments, thesplaying instrument has a capture design for grasping, engaging, orotherwise persuading the cap 1150 to move proximally, out of thereceiver 1110, while the arms 1130 are splayed by the instrument. Or aseparate cap removing instrument, such as one that can fit within,around, or aside of the splaying instrument, can persuade the cap 1150proximally out of the receiver 1110 while the arms 1130 are splayed.Such removing feature or instrument can have an external thread, forinstance, for engaging with the internal thread of the cap 1150.

FIG. 12 is a cross section taken along line 12 of FIG. 11. The viewshows the system 1110 after the setscrew 20 has been threaded into thecap 1150, locking down the rod 10 in the receiver 1110, and locking thecap locking surfaces 1164 against the receiver locking surfaces 1138,thereby preventing unwanted receiver splay.

FIG. 13 is a top, plan, view of the arrangement of FIG. 12, with thesetscrew 20 intact. And FIG. 14 is a perspective view of the arrangementof FIGS. 12 and 13.

Turning to the fourth main related embodiment, FIGS. 15-17 show a system1500 again having a pop-on cap 1550 and receiver 1510. The fourthembodiment is in many ways like the third embodiment. One of the primarydistinctions is that interfacing features of the cap and receiver forrotation-prevention and rotation-resistance for the cap are configureddifferently than those of the third embodiment.

FIG. 15 is a perspective view of the cap 1550 and receiver 1510, priorto popping the cap onto the receiver, according to a fourth embodimentof the present technology.

For initially securing the cap 1550 to the receiver 1510, the cap 1550is lowered toward the receiver 1510 along a system axis 50, as indicatedby arrow. The cap 1550 is orientated for the maneuver withrotation-resisting/rotation preventing wings 1552 aligned, orpositioned, over wing-receiving spaces, or gaps, 1534 of the receiver1510, and/or with distal pop-on/splay-resisting flanges 1560 alignedover the spaces 1534. The cap 1550 is popped onto the receiver 1510 in amanner similar to the pop-on maneuver described above in connection withthe embodiments of FIGS. 2-7.

The cap 1550 and receiver 1510 are further configured (e.g., sized andshaped) such that splaying of the receiver arms 1530 is resisted, in amanner similar to how splaying of the receiver 110 is resisted after cap150 installation was described in connection with the embodiments ofFIGS. 1-9 and 10.

The rotation-resisting/rotation-preventing cap wings 1552 in variousembodiments have a generally rectangular profile, as shown in FIG. 15.The shape can include a lateral surface 1553 and opposing side surfaces1554, for instance. One of each set of side surfaces 1554 isanti-rotation surface 1555. The cap anti-rotation surfaces 1555 abutanti-rotation surfaces 1532 of the receiver, preventing rotation of thecap in a first direction, e.g., clockwise looking distally. In variousembodiments, the end surfaces 1555, though, additional surfaces of thewings 1552 act to prevent rotation. For instance, the lateral surface1553 of each wing 1552 can contact the opposing surface 1539 of thereceiver, further preventing rotation of the cap in the receiver. Insome cases, most, or generally all of the length of the lateral surface1553 can contact the opposing surface 1539 of the receiver, furtherpreventing rotation. A portion of the lateral surface 1553 adjacent orclosest to the interface to the end surface 1555, and adjacent portionof the receiver surface 1539, are in various embodiments where amajority of the rotation-prevention force is focused.

Each cap wing 1552 can also include a sloped or angled distal surface1551. The surface 1551 extends at an angle with respect to an externalside wall 1561 of the cap body of between about 40 and about 50 degrees,in various embodiments. The angle may be generally 45 degrees, forinstance.

The angle in some cases corresponds, such as by being the same or aboutthe same as, to an angle at which a receiver proximal pop-on surface1531 extends with respect to an exterior side wall 1537 of the receiver1510. The corresponding angulation allows the angled distal surface 1551of the cap 1550 to sit more robustly, such as flush or generally flush,with the angled proximal surface 1531, which provides a more-secureseating of the wings 1552, and so the cap 1550, against the proximalreceiver surface 1531, and so against the receiver 1510. An angleddistal wing surface 1551 also allows the cap 1550 to be lowered fartherinto the receiver 1510 than the cap would be able to go distally if thelower outer edge of the wings were square, or more square.

Each cap distal pop-on/splay-resisting flange 1560, and correspondingreceiver features, can be configured in any of the ways thatpop-on/splay-resisting flanges, and corresponding receiver features,were configured in the embodiments of FIGS. 1-14, such as cap flanges160 of FIGS. 1-9. Each flange 1560 can have an angled proximally facingsplay-resisting surface 1564 corresponding to, for interfacing with, adistally facing receiver splay-resisting surface 1538, in the same waythat the flange 160 has the proximally facing surface 164 correspondingfor interface with the distally facing splay-resisting surface 138described in connection with FIG. 2.

The receiver 1510 can further have a proximally facing flange-stop flooror surface 1533. When the cap 1550 is being popped onto the receiver1510, distal surfaces of the cap flanges 1560 abut the stop surface1533, preventing the cap 1550 from moving any farther distally in thereceiver 1510. The surface 1433 can in any way be like the surface 133described in connection with the embodiment of FIG. 2, and vice versa.

In various embodiments, the receiver 1510 has a cap-body receivingcavity 1535. The cavity 1535 allows the cap 1550 to be moved fartherdistally in the receiver 1510, as, if the pop-on surface 1531 wascontinuous, without the cavity 1535 cutout, the side wall 1561 of thecap 1550 would contact the (hypothetical) continuous surface 1531,keeping the cap from moving further distally in the receiver 1510.

The receiver 1510 further includes a cap-flange-receiving cavity 1536.The cavity 1536 can in any way be like the cavity 136 described inconnection with the embodiment of FIG. 2.

As the cap pop-on surfaces 1565 contact and then are pushed fartherdistally against the receiver pop-on surfaces 1531, the cap surfaces1565 slide distally along the receiver surfaces 1531. In this, thereceiver arms 1530 are forced to splay slightly, sufficiently to allowthe cap flanges 1560 to pass the slope 1531. As the flanges clear theslope 1531, contact between the flanges 1560 and slope 1531 is released,and the flanges 1560 enter the receiver cap-receiving cavities 1536 asthe receiver arms 1530 return from being splayed, by natural spring backof the arms 1530.

FIG. 16 is a side cross section of the system 1550 of the fourthembodiment, taken alone line 16-16 of FIG. 15. The view shows the cap1550 having been popped onto the receiver 1510. For the popping on,between the view of FIGS. 15 and 16, a cap pop-on surface 1565, such asa distal/lateral edge or surface, pushes against the receiver pop-onsurface 1531 as the cap 1550 is lowered into contact with the receiver,and then pushed further distally with respect to the receiver. The cappop-on surface 1565 can in any way be like the cap pop-on surface 162described above in connection with FIG. 2, including angulation (angle165) of the surface 1565. Likewise, the receiver pop-on surface 1531 canin any way be like the receiver pop-on surface 134 described above inconnection with the embodiment of FIG. 2, including angulation (angle115) of the surface 132.

When the cap 1550 is popped into the receiver 1510, as shown in FIGS. 16and 17, the cap cannot be turned in a first direction, e.g., clockwiselooking down in FIG. 17. The first-direction rotation is prevented byinterface between the cap anti-rotation surface 1555 and the receiveranti-rotation surface 1532. For instance, when the cap 1550 isinstalled, as shown, and a user threads a setscrew in the firstdirection into the cap 1550, interface between the anti-rotationsurfaces 1555, 1532 abut to keep the cap 1550 from rotating in the samedirection with respect to the receiver 1510. This facilitated setscrewinstallation. A setscrew is not shown in FIGS. 15-17 for thisembodiment, but, again, is shown by way of example in FIGS. 12-14 byreference numeral 20.

When the cap 1550 is popped into the receiver 1510, as shown in FIGS. 16and 17, the splay-resisting surfaces 1564, 1538 of the cap and receiverinterface to prevent splaying absent sufficient splaying force appliedto the receiver arms 1530. The sufficient splaying force is applied byturning the cap in the second direction, e.g., counterclockwise lookingdistally.

Each of the receiver and cap anti-rotation surfaces 1555, 1532 mayextend generally orthogonal to a tangent 1559 of a generally cylindricalbody 1557 of the cap 1550.

The cap wing 1552 and proximal arm 1530 features, including thewing-receiving space 1532, are configured (e.g., sized, shaped, andoriented) such that upon application of at least the predeterminedamount of torque to the cap 1550 in the second direction, the cap 1550rotates in the second direction with respect to the receiver 1510. Inthis cap rotation, a rotation-resisting portion 1556 of the cap 1550sliding along the rotation-resisting surface 1136 of the receiver 1510.The rotation-resisting portion 1556 includes a rotation-resistingsurface, toward an end of the lateral surface 1553 of the wing 1552, inthe area indicated by reference numeral 1556.

Torque can be applied to the cap 1550 in any of a variety of ways toforce intentional splay of the arms 1530. The system 1500 can include orbe used with an instrument or tool (not shown) configured at its distalend to engage a proximal portion of the wings 1552, for instance, andconfigured to apply at least said pre-determined amount of torque to thecap 1550 in the second direction (e.g., counterclockwise), the forcebeing sufficient to overcome friction between the rotation-resistingsurfaces 1556, 1539. The cap surface 1556 can thereby slide with respectto the receiver surface 1539, as described, enabling the cap 1550 torotate with respect to receiver 1510, thereby splaying the arms 1530 forcap removal.

As can be seen in FIGS. 16 and 17, the proximal surface of the wings1552 can extend higher (farther proximally) than an adjacent proximalsurface of the receiver arms 1530. The exposed proximal portion of thecap wings 1552 provides real estate that the instrument can interfacewith to apply torque to the cap 1550 in the second direction. Theinstrument can apply torque against the portion of the anti-rotationsurfaces 1555 of the wings 1552 extending above the arms 1530, forinstance.

A component of forces that the cap rotation-resisting surfaces orportions 1556 apply to adjacent receiver rotation-resisting surfaces1539, sliding in the second direction (e.g., counterclockwise) along thereceiver rotation-resisting surfaces 1539, is a radial force. As theradial force is applied to the receiver rotation-resisting surfaces1539, and thereby to the receiver arms 1530, the arms 1530 areintentionally splayed.

As the receiver arms 1530 of this embodiment are splayed intentionally,the splay-resisting interfaces 1538, 1564 are pushed apart, namely thereceiver splay-resisting surfaces 1538 are forced to move radiallyoutward, along and then off of the cap splay-resisting surface 1564. Thecap 1550 is then free from the receiver 1510, and can be removed in theproximal direction from the receiver 1510. In various embodiments, thesplaying instrument has a capture design for grasping, engaging, orotherwise persuading the cap 1550 to move proximally, out of thereceiver 1510, while the arms 1530 are splayed by the instrument. Or aseparate cap removing instrument, such as one that can fit within,around, or aside of the splaying instrument, can persuade the cap 1550proximally out of the receiver 1510 while the arms 1530 are splayed.Such removing feature or instrument can have an external thread, forinstance, for engaging with the internal thread of the cap 1550.

It should be understood that various aspects disclosed herein may becombined in combinations other than the combinations presentedspecifically in the description and the accompanying drawings. It shouldalso be understood that, depending on the example, certain acts orevents of any of the processes or methods described herein may beperformed in other sequence, added, merged, or left out altogether(e.g., all described acts or events may not be necessary to carry outthe techniques).

In addition, while certain aspects of this disclosure are described asbeing performed by a single module or unit for purposes of clarity, itshould be understood that the techniques of this disclosure may beperformed by a combination of units or modules associated with, forexample, a medical device.

Unless defined specifically otherwise herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc. It must also benoted that, as used in the specification and the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unlessotherwise specified, and that the terms “comprises” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, elements, and/or components, but do not preclude the presenceor addition of one or more other features, steps, operations, elements,components, and/or groups thereof.

It will be understood that various modifications may be made to theembodiments disclosed herein. Therefore, the above description shouldnot be construed as limiting, but merely as exemplification of thevarious embodiments. Those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

1. A system for use in spinal surgery, comprising: a cap having acylindrical body extending along a first longitudinal axis betweenopposite proximal and distal ends, the body comprising a set of opposingsplay-resisting flanges and a set of wings, the flanges and the wingseach extending radially from the distal end about the first longitudinalaxis in a plane extending perpendicular to the first longitudinal axis,the wings each being positioned between the flanges such that wings arespaced apart from the flanges; and a receiver having opposing armsspaced equally from a second longitudinal axis of the receiver, each armextending to a respective proximal end from a common distal base, eacharm having an inner proximal protrusion at or adjacent the proximal end,and each arm having an inner sloped splaying surface distal of theproximal protrusion; wherein: each cap flange has a proximal-facing capsplay-prevent surface, sloped proximally and radially outward, and adistal-facing cap pop-on surface; each receiver proximal protrusion has(i) a proximal-facing sloped receiver pop-on surface extending distallyand radially inward toward the second longitudinal axis, and (ii) adistal-facing sloped receiver splay-prevent surface extending distallyand radially inward toward the second longitudinal axis; the receiverpop-on surfaces are spaced from each other such that each cap pop-onsurface contacts a respective one of the receiver pop-on surfaces whenthe cap is centered on the second longitudinal axis and moved distallyto contact the receiver; and each inner sloped splaying surface extendsdistally and radially inward toward the second longitudinal axis andinto a cylindrical plane defined by an inner diameter of the cap.
 2. Thesystem of claim 1, wherein the inner diameter of the cap is greater thana width of a spinal-correction rod that the receiver is configured tohold in use of the system.
 3. The system of claim 2, wherein the innerdiameter of the cap is between 0.5 mm and 2.0 mm larger than an outerdiameter of the spinal-correction rod.
 4. The system of claim 2, whereineach splaying surface extends radially inward into the cylindrical planeby a radial distance of between 0.5 mm and 2.0 mm short of an outerdiameter of the spinal-correction rod.
 5. The system of claim 1, whereineach sloped splaying surface extends at an angle with respect to ahorizontal reference frame of between 35 degrees and 55 degrees.
 6. Thesystem of claim 1, wherein: each cap splay-prevent surface extends at acap splay-prevent angle with respect to a horizontal reference frame ofbetween 5 degrees and 75 degrees; and each receiver splay-preventsurface extends at a receiver splay-prevent angle with respect to thehorizontal reference frame of between 5 degrees and 75 degrees.
 7. Thesystem of claim 6, wherein: each cap splay-prevent angle is between 10degrees and 45 degrees; and each receiver splay-prevent angle is between10 degrees and 45 degrees.
 8. The system of claim 1, wherein eachreceiver pop-on surface extends at a receiver pop-on angle with respectto a horizontal reference frame of between 50 degrees and 80 degrees. 9.The system of claim 1, wherein; the receiver pop-on surfaces are spacedfrom each other such that each cap pop-on surface contacts a respectiveone of the receiver pop-on surfaces when the cap is centered on thesecond longitudinal axis, with the cap wings aligned between thereceiver arms, and moved distally to contact the receiver.
 10. Thesystem of claim 9, wherein: each receiver arm extends between opposinglateral edges; lateral edges of each arm, of the set of arms, are spacedby an inter-arm distance from an adjacent lateral edge of the other arm,of the set of arms; and each cap wing has a width that is generallyequal to, but slightly smaller than, the inter-arm distance, to allowthe cap wing to be slid distally between the receiver arms and contactboth adjacent lateral arm edges when the wings are positioned betweenthe arms and torque is applied to the cap.
 11. The system of claim 1,wherein: each receiver arm has an inner surface extending from a distalportion to a proximal portion adjacent said proximal end of the arm; andthe proximal portion of each inner surface defines a protrusion cavityreceiving the cap flange when the cap is popped onto the receiver. 12.The system of claim 1, wherein the wings extend from body orthogonallyto a line along which the flanges extend from the body.
 13. A system foruse in spinal surgery, comprising: a cap for being popped onto a rodreceiver, the cap having a cylindrical body extending along a firstlongitudinal axis between opposite proximal and distal ends, the bodycomprising a set of opposing flanges and a set of opposing wings, theflanges and the wings extending radially from the distal end about thefirst longitudinal axis in a plane extending perpendicular to the firstlongitudinal axis, the wings each being positioned between the flangessuch that wings are spaced apart from the flanges; and the receiverhaving opposing arms spaced equally from a second longitudinal axis ofthe receiver, each arm extending to a respective proximal end from acommon distal base, each arm having an inner proximal protrusion at oradjacent the proximal end, each arm having an inner sloped splayingsurface distal of the proximal protrusion, each receiver proximalprotrusion having (i) a proximal-facing sloped receiver pop-on surfaceextending distally and radially inward toward the second longitudinalaxis, and (ii) a distal-facing sloped receiver splay-prevent surfaceextending distally and radially inward toward the second longitudinalaxis, the receiver pop-on surfaces being spaced from each other suchthat each cap pop-on surface contacts a respective one of the receiverpop-on surfaces when the cap is centered on the second longitudinal axisand moved distally to contact the receiver, and each inner slopedsplaying surface extending distally and radially inward toward thesecond longitudinal axis and into a cylindrical plane defined by aninner diameter of the cap; wherein each cap flange has a proximal-facingcap splay-prevent surface, sloped proximally and radially outward, and adistal-facing cap pop-on surface.
 14. The system of claim 13, whereinthe inner diameter of the cap is greater than a width of aspinal-correction rod that the receiver is configured to hold in use ofthe system.
 15. The system of claim 13, wherein the inner diameter ofthe cap is between 0.5 mm and 2.0 mm larger than an outer diameter ofthe spinal-correction rod.
 16. The system of claim 13, wherein eachsplaying surface extends radially inward into the cylindrical plane by aradial distance of between 0.5 mm and 2.0 mm short of an outer diameterof the spinal-correction rod.
 17. The system of claim 13, wherein; thereceiver pop-on surfaces are spaced from each other such that each cappop-on surface contacts a respective one of the receiver pop-on surfaceswhen the cap is centered on the second longitudinal axis, with the capwings aligned between the receiver arms, and moved distally to contactthe receiver.
 18. A system for use in spinal surgery, comprising: areceiver for receiving a pop-on cap, the receiver having opposing armsspaced equally from a first longitudinal axis of the receiver, each armextending to a respective proximal end from a common distal base, eacharm having an inner proximal protrusion at or adjacent the proximal end,and each arm having an inner sloped splaying surface distal of theproximal protrusion; the cap having a cylindrical body extending along asecond longitudinal axis between opposite proximal and distal ends, thebody comprising a set of opposing flanges and a set of opposing wings,the flanges and the wings extending radially from the distal end aboutthe second longitudinal axis in a plane extending perpendicular to thesecond longitudinal axis, the wings each being positioned between theflanges such that wings are spaced apart from the flanges, each capflange having a proximal-facing cap splay-prevent surface, slopedproximally and radially outward, and a distal-facing cap pop-on surface;wherein: each receiver proximal protrusion has (i) a proximal-facingsloped receiver pop-on surface extending distally and radially inwardtoward the first longitudinal axis, and (ii) a distal-facing slopedreceiver splay-prevent surface extending distally and radially inwardtoward the first longitudinal axis; the receiver pop-on surfaces arespaced from each other such that each cap pop-on surface contacts arespective one of the receiver pop-on surfaces when the cap is centeredon the first longitudinal axis and moved distally to contact thereceiver; and each inner sloped splaying surface extends distally andradially inward toward the first longitudinal axis and into acylindrical plane defined by an inner diameter of the cap.
 19. Thesystem of claim 18, wherein: each splaying surface has a radial-most anddistal ends; and each splaying surface is sized and oriented such thatthe distal end contacts a spinal-correction rod that the receiver isconfigured to hold in use of the system.
 20. The system of claim 19,wherein each splaying surface extends radially inward into thecylindrical plane by a radial distance of between 0.5 mm and 2.0 mmshort of an outer diameter of the spinal-correction rod.
 21. The systemof claim 18, wherein each sloped splaying surface extends at an anglewith respect to a horizontal reference frame of between 35 degrees and55 degrees.